Image scanner having contact-type image sensor movable under automatic document feeder

ABSTRACT

There is provided an image scanner in which no shock is applied to a carrier moving an image sensor when the carrier is moved between an automatic document feeder and a contact glass on which an original document is placed. The image sensor is pressed against the contact glass by a spring, A plurality of rollers are provided between the image sensor and the contact glass so that the image sensor is pressed against the contact glass via the rollers. The rollers are separated from the contact glass by a separating member when the image sensor passes an area between the contact glass and the automatic document feeder.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to image scanning apparatusesused in copy machines or facsimile machines, and more particularly to animage scanning apparatus having a contact-type image sensor to scan anoriginal image.

2. Description of the Prior Art

A CCD image sensor or a contact-type image sensor is commonly used in aconventional image scanner (image reading apparatus). In an imagescanner applicable for scanning a book which image scanner can scan anoriginal document of which position is fixed on a contact glass, athickness of the image scanner can be reduced by using the contact-typeimage sensor rather than the CCD image sensor. Additionally, usage ofthe contact-type image sensor has advantages in that a driving systemthereof is greatly simplified such that most adjustments are not needed,and a distortion of an image due to an optical reduction system is notgenerated because the contact-type image sensor does not use the opticalreduction system.

However, although the contact-type image sensor has the above-mentionedadvantages, there is a problem in that a constant position of a focalpoint is not obtained over an entire scanning area unless a supportingconstruction of the image sensor has a high accuracy and rigidity.

In order to eliminate the above-mentioned problem, Japanese Laid-OpenPatent Application No. 3-276958 suggests an image scanner having acontact-type image sensor in which the image scanner maintains aconstant distance between a carriage base having the image sensor and acontact glass supporting the original document, thereby maintaining aconstant focal point over the entire scanning area. In order to maintaina constant distance, one of sides of the carriage base is pressedagainst the contact glass by interposing a spacer mechanism, comprisingsuch as a roller, between the carriage base and the contact glass.

When an automatic document feeder (ADF) is provided to theabove-mentioned image scanner, and if the ADF is placed on a singlecontact glass in an area different from an area in which a scanningfunction of the book scanning is provided, no problem may occur inmoving the contact-type image sensor while the carriage base having theimage sensor is pressed against the contact glass. However, in such acase, the ADF must be placed on the contact glass, that is, conveyingrollers of the ADF cannot be placed below the contact glass, and thus anentire construction of the image scanner becomes large. Additionally, ifthe ADF is merely placed on the contact glass as shown in FIG. 1, aguide member 1 of the ADF may protrudes from a top surface of thecontact glass 2 in a conveying path 3 as indicated by chain lines inFIG. 1, and thus a leading edge of an original document sheet may becaught by the protrusion formed by the guide member 1. In order toeliminate such a problem, a recess 4 is formed in the top surface of thecontact glass 2 to accommodate the guide member 1 so that no protrusionis formed in the conveying path 3. However, it is difficult andinconvenient to form the recess 4 in the top surface of the contactglass 2.

In order to eliminate a formation of the recess 4 in the contact glass2, the image scanner may have two separate contact glasses, the carriagehaving the contact-type image sensor being moved over the two contactglasses while it is pressed against the two contact glasses. However, insuch a case, a step or a gap may be formed between the two contactglasses, and thereby a shock may be applied to the spacer mechanism ofthe carriage having the contact-type image sensor in an area between thetwo contact glasses. Accordingly, there is a problem in that thecontact-type image sensor or a spacer mechanism may become damaged aftera long time of use during which the shock is applied repeatedly thereto.

Additionally, in the image scanner (hereinafter referred to as a bookimage scanner) in which an image sensor is moved under a contact glasson which an original document, such as an opened page of a book, isplaced, a contact-type image sensor having a short focus, comprisingsuch as a rod lens array, is commonly used because of an advantage ofminiaturization. However, such an image sensor has a small marginagainst a displacement of a focal point because of its short focaldistance. That is, in the image sensor having a rod lens array, anoptical path from an image to a light detecting element extends in adirection parallel to a direction of a thickness of the image sensor,and thus a focal distance of the rod lens array is relatively short.Accordingly, if a position of the original document in a directionperpendicular to the top surface of the contact glass is not constant,or if a thickness of the contact glass is not uniform, there may be aproblem in that a well-focused image is not obtained.

When the contact-type image sensor is used in the book image scanner, alevel of the focal point relative to the contact glass must be uniformover an entire area where the image sensor is moved, and thus a highaccuracy and rigidity are required for a construction of the imagescanner. Accordingly, an entire construction of the image scannerbecomes large and heavy although the contact-type image sensor, which issmall and thin, is used in the image scanner.

SUMMARY OF THE INVENTION

It is a general object of the present invention to provide an imagescanner having a contact-type image sensor in which image scanner theabove-mentioned disadvantages are eliminated.

A more specific object of the present invention is to provide an imagescanner having a contact-type image sensor in which image scanner noshock is applied to a carrier moving the image sensor when the carrieris moved between an area in which an automatic document feeder isprovided and an area in which an original document is scanned by beingplaced on a contact glass.

Another object of the present invention is to provide an image scannerhaving a contact-type image sensor having a large focal depth so that agood focus is obtained even if a position of the original document in adirection perpendicular to a top surface of a contact glass is notconstant.

In order to achieve the above-mentioned objects, there is providedaccording to one aspect of the present invention an image scannercomprising:

a first contact glass on which a first original document is placed, thefirst contact glass having a first bottom surface opposite to a surfaceon which the first original document is placed;

an automatic document feeder having a second contact glass through whicha second original document fed through the inside of the automaticdocument feeder is scanned, the automatic document feeder having asecond bottom surface opposite to a side on which the second originaldocument is fed, wherein the first bottom surface of the first contactglass and the second bottom surface of the second contact glass lie inthe same plane;

an image sensor scanning the first original document while moving underthe first contact glass, the image sensor scanning the second originaldocument by moving to a fixed position directly under the second contactglass;

spacer means, provided on the image sensor, maintaining a distancebetween the image sensor and the first contact glass to be constant bycontacting the first bottom surface of the first contact glass when theimage sensor is scanning the first original document, the spacer meansmaintaining a distance between the image sensor and the second contactglass to be constant by contacting the second bottom surface of thesecond contact glass when the image sensor is scanning the secondoriginal document;

pressing means for pressing the image sensor via the spacer meansagainst the first bottom surface of the first contact glass when theimage sensor is scanning the first original document, and for pressingthe image sensor via the spacer means against the second bottom surfaceof the second contact glass when the image sensor is scanning the secondoriginal document; and

separating means for separating the spacer means from the first bottomsurface of the first contact glass when the image sensor is moved from aposition under the first contact glass to the fixed position under thesecond contact glass, and for separating the spacer means from thesecond bottom surface of the second contact glass when the image sensoris moved from the fixed position under the second contact glass to aposition under the first contact glass.

Additionally, there is provided according to another aspect of thepresent invention an image scanner comprising:

a contact glass on which an original document is placed, the contactglass having a bottom surface opposite to a surface on which theoriginal document is placed;

an image sensor scanning the original document while moving under thecontact glass, the image sensor having an optical system which projectsa light beam onto the original document placed on the contact glass andreceives the light beam reflected by the original document, the lightbeam reflected by the original document being focused on a lightreceiving element provided in the optical system, a length of an opticalpath between the original document and the light receiving element beinggreater than a distance between the original document and the lightreceiving element;

spacer means, provided on the image sensor, maintaining a distancebetween the image sensor and the contact glass to be constant bycontacting the bottom surface of the contact glass when the image sensoris scanning the original document; and

pressing means for pressing the image sensor via the spacer meansagainst the bottom surface of the contact glass when the image sensor isscanning the original document.

Other objects, features and advantages of the present invention willbecome more apparent from the following detailed description when readin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view inside a conventional automatic document feeder;

FIG. 2 is a cross-sectional view of the first embodiment of an imagescanner according to the present invention;

FIG. 3 is a cross-sectional view taken along a line III--III in FIG. 2;

FIG. 4 is a side view of an essential part of a second embodiment of animage scanner according to the present invention;

FIGS. 5A and 5B are side views showing an essential part of a thirdembodiment of an image scanner according to the present invention;

FIG. 6 is a side view of an essential part of a fourth embodimentaccording to the present invention;

FIG. 7 is a side view of a supporting construction of an image sensor ina fifth embodiment of an image scanner according to the presentinvention;

FIG. 8 is a front view of the supporting construction shown in FIG. 7;

FIG. 9 is a perspective view of the supporting construction shown inFIG. 7;

FIG. 10 is a cross-sectional view of a contact-type image sensor, whichis an essential part of the fifth embodiment of an image scanneraccording to the present invention; and

FIG. 11 is a perspective view of an optical system provided in the imagesensor shown in FIG. 10.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description will now be given of a first embodiment of an imagescanner according to the present invention. FIG. 2 is a cross-sectionalview of the first embodiment of the image scanner according to thepresent invention. FIG. 3 is a cross-sectional view taken along a lineIII--III in FIG. 2.

In FIGS. 2 and 3, the first embodiment of the image scanner according tothe present invention comprises a main body 11, a contact glass 12, anautomatic document feeder (ADF) 13, a carriage 14 having a contact-typeimage sensor 15 and a guide shaft 16. The contact glass 12 is fixed on atop of the main body 11, and an original document to be scanned isplaced thereon. The ADF 13 is positioned on a top of the main body 11and is adjacent to the contact glass 12. The carriage 14 on which thecontact-type image sensor 15 is mounted is moved in an area positionedunder the contact glass 12 and the ADF 13. The movement of the carrier14 is guided by the guide shaft 16 provided in the main body 11.

The ADF 13 is a single unit comprising a supplying roller 21, aplurality of conveying rollers 22, guide plates 23 and a contact glass24. The supplying roller 21 feeds original documents placed in a supplytray 20 into the ADF 13 one by one. Each original document fed into theADF 13 is conveyed and guided by the conveying rollers 22 and guideplates 23 so that the original document passes over the contact glass 24through which the original document is scanned by the contact-type imagesensor 15. The ADF 13 is easily handled and removed from the main body11 as it is packed into a single unit.

The carriage 14 is supported, as shown in FIG. 3, by the guide shaft 16on one side thereof, and a sliding protrusion 26 is formed on the otherside thereof. The sliding protrusion 26 slides on a rail member 25formed on the main body 11. The carriage 14 is driven by a wire 27 ofwhich opposite ends are connected to the carriage 14. The wire 27 ishalf wound on a pulley 28, and the pulley 28 is rotated by a reversiblemotor 29. Accordingly, the carriage 14 can be reciprocally moved bydriving forces generated by the reversible motor 29 and transmittedthrough the pulley 28 and the wire 27.

The contact-type image sensor 15 moves under the contact glass 12 ormoves to a position directly under the contact glass 24 of the ADF 13 soas to scan an image of an original document placed on the contact glass12 or an original document fed through the ADF 13, respectively. Rollers30, which act as spacers, are rotatably supported on an upper portion ofthe image sensor 15. Additionally, a side wing 33 is mounted on each ofside surfaces of the image sensor 15 which side surfaces are parallel toan axis of the guide shaft 16, and a wing portion 33a extends from theside wing 33. The wing portion 33a of the side wing 30 has a throughhole into which a shaft 31 protrusively provided on the carriage 14 isinserted. A spring 32 is fit on the shaft 32 between the carriage 14 andthe wing portion 33a of the side wing 33 so that the spring 32 pressesthe image sensor 15 toward a bottom surface of the contact glass 12 orthe contact glass 24.

Racks 35 are attached on one of surfaces facing in moving directions ofthe carriage 14. A motor 36 is fixed on the carriage 14 which motor 36has an output shaft of which opposite ends are provided with piniongears 37 engaging with the respective racks 35. Each of the pinion gears37 has teeth on only a part of its periphery, and thus the pinion gears37 engage with the respective racks 35 only when the teeth are rotatedto a predetermined position. FIG. 2 shows a state in which the teeth ofthe pinion gears 37 are not engaged with the racks 37. The pinion gears37 are rotated when the motor 36 is driven, and engages with the racks35 to move the image sensor downward. Accordingly, the racks 35, thepinion gears 37 and the motor 36 constitute separating means, the racks35 and the pinion gears 37 together correspond to a driving unit, andthe motor 36 corresponds to a driving power source.

In the above-mentioned construction, when an original document placed onthe contact glass 12 is scanned, the carriage 14 moves under the contactglass 12 by being pulled by the wire 27 while a distance between theimage sensor 15 and the bottom surface of the contact glass 12 ismaintained to be constant as the image sensor 15 is pressed against thecontact glass 12 via the rollers 30 interposed therebetween. Thescanning of the original document is performed while the carriage 14 ismoving.

When the carriage 14 and thus the image sensor 15 moves from an areaunder the contact glass 12 to an area directly under the contact glass24 to perform a scanning operation of an original document fed throughthe ADF 13, the pinion gears 37 are rotated by the motor 36 in adirection indicated by an arrow near the pinion gear 37 in FIG. 2. Asthe pinion gears 37 rotate toward the racks 35, the teeth of the piniongears 37 are engaged with the respective racks 35, and thus the imagesensor 15 is moved downward, resulting in the rollers 30 mounted on theimage sensor 15 separating from the bottom surface of the contact glass12.

In the above-mentioned state in which the rollers 30 are separated fromthe contact glass 12, the carriage 14 is moved directly under thecontact glass 24 of the ADF 13. In this state, the motor 36 is reversedto disengage the teeth of the pinion gears 37 from the racks 35. Theimage sensor 15 is thereby moved by the springs 32 toward the contactglass 24, and thus the rollers 30 contact the contact glass 24. In thiscondition, the distance the same as the distance when the image sensor15 is under the contact glass 12 is provided between the image sensor 15and the contact glass 24. After the rollers 30 contact the contact glass24, the ADF 13 is operated to feed the original document therethrough,and then a scanning operation of the image sensor 15 is started whilethe image sensor is maintained to be at a fixed position directly underthe contact glass 24.

When the image sensor 15 is moved from the fixed position under thecontact glass 24 to the area under the contact glass 12 to performanother scanning operation, similar processes are taken to separate therollers 30 from the contact glass 24.

Accordingly, the rollers 30 never contact an area between the contactglass 12 and the contact glass 24 in which area a step or a gap isformed. Thus, no shock is applied to the image sensor 15 and thecarriage 14, providing a constant level of a focal point over a longtime.

A description will now be given of a second embodiment of an imagescanner according to the present invention. FIG. 4 is a side view of anessential part of the second embodiment of the image scanner accordingto the present invention. In FIG. 4, parts that are the same as theparts shown in FIGS. 2 and 3 are given the same reference numerals, anddescriptions thereof will be omitted.

In the second embodiment, the rack and pinion mechanism of the firstembodiment is replaced with a linear actuator comprising a solenoid 41.The solenoid 41 is fixed to the carriage 14, and a plunger 40 isextended from the solenoid 41. The end of the plunger 40 engages with anarm member 42 extending from a side surface of the image sensor 15. Whenthe solenoid 41 is activated, the plunger 40 is attracted into thesolenoid 41, and thus the image sensor 15 is moved downwardly toseparate the rollers 30 from the contact glass 12 or the contact glass24. In this embodiment, because no gear mechanism is provided, there isno noise due to the gear mechanism, and thus up and down operations ofthe image sensor 15 can be performed with relatively low noise.

A description will now be given, with reference to FIGS. 5A and 5B, of athird embodiment of the image scanner according to the presentinvention. FIGS. 5A and 5B are side views showing an essential part ofthe third embodiment of an image scanner according to the presentinvention. In FIGS. 5A and 5B, parts that are the same as the partsshown in FIGS. 2 and 3 are given the same numerals, and descriptionsthereof will be omitted.

In the third embodiment, no mechanical separating means is provided asis in the first and second embodiments, and instead a protruding member46 is merely provided under an area 45 between the contact glass 12 anda bottom surface of the ADF 13 which bottom surface is in the same levelwith the bottom surface of the contact glass 24. When the image sensor15 moves under the area 45, the image sensor 15 is moved downward as theimage sensor 15 is forced underneath the protruding member 46, and thusthe rollers 30 are separated from the contact glass 12 or the contactglass 24. Accordingly, no shock is applied to the rollers 30 when thecarriage moves under the area 45 between the contact glass 12 and theADF 13. The protruding member 46 may be placed so that a top surface ofeach of the side wings 33 is forced underneath the protruding member 46.A corner 33c of each of the side wings 33 is rounded so that the sidewings 33 can smoothly move underneath the protruding member 46. A slopemay be formed on the corners 33c of the side wings 33 instead ofproviding a roundness. Additionally, the protruding member 46 may befixed on a bottom surface of the ADF 13 so that the protruding member 46is automatically placed in an area adjacent to the area 45 when the ADF13 is attached to the image scanner.

A construction of the third embodiment is achieved at a reduced costbecause no mechanical means is provided to separate the rollers 30 fromthe contact glass 12 or the bottom surface of the ADF 13. Additionally,the carriage 14 can be made small since an area in which themechanically separating means is provided is not needed in the carriage14.

A description will now be given, with reference to FIG. 6, of a fourthembodiment of an image scanner according to the present invention. FIG.6 is a side view of an essential part of the fourth embodiment of theimage scanner according to the present invention. In FIG. 6, parts thatare the same as the parts shown in FIGS. 2 and 3 are given the samereference numerals, and descriptions thereof will be omitted.

In the fourth embodiment, a sheet 50 made of a thin plate is provided inthe area 45 instead of the protruding member 46 of the above-mentionedthird embodiment. That is, the sheet 50 covers a gap or a step formed inthe area 45 so that the rollers 30 are forced underneath the sheet 50when the carriage passes the under the area 45 between the contact glass12 and the ADF 13. According to the present embodiment, a shock appliedto the rollers 30 is minimized due to the sheet 50 to protect the outersurfaces of the rollers 30 from being damaged. Since the sheet 50 ismerely applied to the area 45, the present embodiment can reduce theshock applied to the rollers 30 with a reduced cost.

A description will now be given of a fifth embodiment of an imagescanner according to the present invention. FIG. 7 is a side view of asupporting construction of the image sensor 15 in the fifth embodiment.FIG. 8 is a front view of the supporting construction shown in FIG. 7.FIG. 9 is a perspective view of the supporting construction shown inFIG. 7. In FIGS. 7 to 9, parts that are the same as the parts shown inFIGS. 2 and 3 are given the same reference numerals, and descriptionsthereof will be omitted.

In the fifth embodiment, an image sensor 15 is supported by the sameconstruction as that of the first embodiment as shown in FIGS. 7 to 9.Accordingly, the image sensor 15 is pressed against a contact glass 12with rollers 30 positioned therebetween.

FIG. 10 is a cross-sectional view of the contact-type image sensor 15,which is an essential part of the fifth embodiment of the image scanneraccording to the present invention. In FIG. 10, parts that are the sameas the parts shown in FIGS. 2 and 3 are given the same referencenumerals, and descriptions thereof will be omitted. It should be notedthat parts of the fifth embodiment, which parts are not shown in FIG.10, are the same as that of the above-mentioned first to fourthembodiments.

The image sensor 15 of the fifth embodiment comprises a sensor frame 60,a light source 61, a roof mirror lens array (RMLA) 62, a deflectionmirror 63 and light receiving elements 64 provided on a sensor substrate65. The RMLA 62 may be an equal-magnification image forming elementarray.

FIG. 11 is a perspective view of an optical system provided in the imagesensor 15. The RMLA 62 comprises a roof mirror array 70 and a lens array72. The roof mirror array 70 has a plurality of roof mirrors 71 arrangedon a straight line. The lens array 72 has a plurality of lenses 73aligned with the straight line on which the roof mirrors 71 arearranged. An aperture plate 74 (not shown in FIG. 11) is providedbetween the roof mirror array 70 and the lens array 72.

In the image sensor 15, a light beam is projected onto an originaldocument placed on the contact glass 12 (or the contact glass 24)through the contact glass 12, and the light beam reflected by theoriginal document returns inside the image sensor 15. The light beamreturned inside the image sensor 15 passes through the optical systemprovided in the image sensor 15, and is finally incident on the lightreceiving elements 64. More specifically, the light beam returned theimage sensor 15 is incident on one of the lenses 73 of the lens array 72first. The light beam passes through the one of the lenses 73, isreflected by the corresponding one of the roof mirrors 71, and returnsto the one of the lenses 73. The light beam passed through twice the oneof the lenses 73 is then reflected by the split mirror 63 toward acorresponding one of the light receiving elements 64. That is, the lightbeam incident on the deflection mirror 63 is deflected approximately 90degrees.

In the above-mentioned optical system of the present embodiment, thelens array 72, the roof mirror array 70, the deflection mirror 63 andthe light receiving elements 64 are arranged so that the light beamreflected by the original document is focused on a focal plane in whichlight receiving surfaces of the light receiving elements 64 arearranged. Since the optical path of the light beam from the lens array72 to the focal plane on the light receiving elements 64 is folded bythe roof mirror array 70 and bent by the deflection mirror 63, thesubstantial focal distance between the optical center of the lens array73 and the focal plane of the light receiving elements 64 is longer thanthat of the optical path which is not folded by a mirror. Accordingly, agreater focal depth can be obtained by the present embodiment, and thusa margin to a displacement of the original document in a directionperpendicular to the top surface of the contact glass 12 becomes large.

It should be noted that a focal point of the lens array 72 is positionedat a position indicated by an "X" located inside the contact glass 12 sothat the light beam passed through said contact glass 12 is focused on atop surface of said contact glass on which the original document to bescanned is placed.

In the above-mentioned fifth embodiment, the contact-type image sensor15 having a small thickness with a large focal depth is used withrollers 30 which act to maintain a distance between the contact glass 12and the image sensor 15 as small as possible. Accordingly, a highaccuracy and rigidity are not required for an entire construction of theimage scanner, and thus a thickness and a weight of the image scannerare greatly reduced.

The present invention is not limited to the specifically disclosedembodiments, and variations and modifications may be made withoutdeparting from the scope of the present invention.

What is claimed is:
 1. An image scanner comprising:a first contact glasson which a first original document is placed, said first contact glasshaving a first bottom surface opposite to a surface on which said firstoriginal document is placed; an automatic document feeder having asecond contact glass through which a second original document fedthrough the inside of the automatic document feeder is scanned, saidautomatic document feeder having a second bottom surface opposite to aside on which said second original document is fed, wherein said firstbottom surface of said first contact glass and said second bottomsurface of said second contact glass lie in the same plane; an imagesensor scanning said first original document while moving under saidfirst contact glass, said image sensor scanning said second originaldocument by moving to a fixed position directly under said secondcontact glass; spacer means, provided on said image sensor, maintaininga distance between said image sensor and said first contact glass to beconstant by contacting said first bottom surface of said first contactglass when said image sensor is scanning said first original document,said spacer means maintaining a distance between said image sensor andsaid second contact glass to be constant by contacting said secondbottom surface of said second contact glass when said image sensor isscanning said second original document; pressing means for pressing saidimage sensor via said spacer means against said first bottom surface ofsaid first contact glass when said image sensor is scanning said firstoriginal document, and for pressing said image sensor via said spacermeans against said second bottom surface of said second contact glasswhen said image sensor is scanning said second original document; andseparating means for separating said spacer means from said first bottomsurface of said first contact glass when said image sensor is moved froma position under said first contact glass to said fixed position undersaid second contact glass, and for separating said spacer means fromsaid second bottom surface of said second contact glass when said imagesensor is moved from said fixed position under said second contact glassto a position under said first contact glass.
 2. The image scanner asclaimed in claim 1, wherein said spacer means comprises a plurality ofrollers provided on said image sensor so that said rollers roll on saidfirst bottom surface of said first contact glass when said image sensoris moved under said first contact glass.
 3. The image scanner as claimedin claim 1, wherein said separating means comprises a driving unit whichmoves said image sensor downward and a power unit supplying a drivingpower to said driving unit.
 4. The image scanner as claimed in claim 3,wherein said power unit comprises a rotary actuator.
 5. The imagescanner as claimed in claim 4, wherein said driving unit comprises arack and a pinion gear engaging with said rack.
 6. The image scanner asclaimed in claim 5, wherein said pinion gear has teeth on only a part ofa periphery thereof.
 7. The image scanner as claimed in claim 3, whereinsaid power unit comprises a linear actuator.
 8. The image scanner asclaimed in claim 7, wherein said linear actuator comprises a solenoidand a plunger reciprocally provided in said solenoid.
 9. The imagescanner as claimed in claim 1, wherein said separating means comprises aprotruding member provided under an area between said first contactglass and a third bottom surface of said automatic document feeder, saidthird bottom surface including said second bottom surface of said secondcontact glass, said image sensor being moved underneath said protrudingmember when said image sensor is moved under said area so that saidimage sensor is pressed down by said protruding member.
 10. The imagesensor as claimed in claim 9, wherein said protruding member is fixed onsaid automatic document feeder.
 11. The image scanner as claimed inclaim 1, wherein said separating means comprises a thin plate providedunder an area between said first contact glass and a third bottomsurface of said automatic document feeder, said third bottom surfaceincluding said second bottom surface of said second contact glass, saidspacer means being moved underneath said thin plate when said imagesensor is moved under said area.
 12. An image scanner as claimed inclaim 1, whereinsaid image sensor having an optical system whichprojects a light beam onto said original document placed on said firstcontact glass and receives the light beam reflected by said originaldocument, the light beam reflected by said original document beingfocused on a light receiving element provided in said optical system, alength of an optical path between said original document and said lightreceiving element being greater than a distance between said originaldocument and said light receiving element.
 13. The image scanner asclaimed in claim 12, wherein said spacer means comprises a plurality ofrollers provided on said image sensor so that said rollers roll on saidfirst bottom surface of said first contact glass when said image sensoris moved under said first contact glass.
 14. The image scanner asclaimed in claim 12, wherein said optical system of said image sensorcomprises:a lens array having a plurality of lenses aligned with apredetermined pitch; a roof mirror array having a plurality of roofmirrors arranged correspondingly to said lenses, a number of said lensesbeing equal to a number of said roof mirrors, one of said roof mirrorsreflecting the light beam passed through a corresponding one of saidlenses and returning the light beam to said corresponding one of saidlenses; and a deflecting mirror deflecting the light beam twice passedthrough said corresponding one of said lenses to said light receivingelement.
 15. The image scanner as claimed in claim 14, wherein a focalpoint of said optical system of said image sensor is positioned insidesaid first contact glass so that the light beam passed through saidfirst contact glass is focused on a top surface of said first contactglass.